fix: Fix timestamp proto util to default to timestamp at call time. (#…

…933)

* fix: Fix timestamp proto util to default to timestamp at call time.

* chore: lint

google/cloud/aiplatform/utils/__init__.py

@@ -617,15 +617,17 @@ def _timestamped_copy_to_gcs(
 
 
 def get_timestamp_proto(
-    time: Optional[datetime.datetime] = datetime.datetime.now(),
+    time: Optional[datetime.datetime] = None,
 ) -> timestamp_pb2.Timestamp:
     """Gets timestamp proto of a given time.
     Args:
         time (datetime.datetime):
-            Required. A user provided time. Default to datetime.datetime.now() if not given.
+            Optional. A user provided time. Default to datetime.datetime.now() if not given.
     Returns:
-        timestamp_pb2.Timestamp - timestamp proto of the given time, not have higher than millisecond precision.
+        timestamp_pb2.Timestamp: timestamp proto of the given time, not have higher than millisecond precision.
     """
+    if not time:
+        time = datetime.datetime.now()
     t = time.timestamp()
     seconds = int(t)
     # must not have higher than millisecond precision.